Spectrogram plot - help required

Hi, I have no clue if this is a repetition. I need help to get the spectrogram of a signal which I have generated. My signal is somewhat like this, It has frequencies from 100 Hz to 7100 Hz in steps of 500 Hz. Like [100,600,1100,...,7100]. So 15 frequencies in total. An interval of 0.1 secs has a constant frequency. So the signal stretches from 0 to 1.5 secs. Each interval of 0.1 secs has a frequency from the vetor which I stated before. The signal is 'A*sin(2*pi*(F/Fs)*n)' where F-freq of the signal and Fs-sampling freq. the frequency of the signal in the interval 0 to 0.1 is F/Fs=100Hz and from 0.1 to 0.2 is 200Hz. sampling frequency used is 8000Hz. I have made sure that each interval of 0.1 sec contains 512 samples. Now I'm choosing a window of length 512, FFT length 512, noverlap is empty, Fs = 8KHz, and finally 'x' is a row vector containing (15*512) values. Is this right what I'm doing?

B=spectrogram(signalvector of dim 1*7680,512,[],512,8000);

this B matrix has dim of 257*29. I don't get the meaning of that either. I do not even know how to get the spectrogram map. The help menu was sounding Latin for me. Please help me with how to plot a spectrogram of the signal I have generated.

Please help!